SystemC Kernel Time Stamp

Let's use an EDS kernel with its tnow variable defined
by the head of the event queue. This is our main reference time stamp,
but let's try not to use the kernel very much, only entering it
when inter-module communication is needed.
This reduces context swap overhead (I know it's all in user space but
it is a computed branch that does not get predicted) and
we can run a large number of ISS instructions at one time, giving good
use of the caches on the modelling workstation.